Pneumatic springs, commonly referred to as air springs, have been used with motor vehicles for a number of years to provide cushioning between movable parts of the vehicle primarily to absorb shock loads impressed on the vehicle axles by the wheels striking an object in the road or falling into a depression. These air springs usually consist of a flexible rubber sleeve or bellows containing a supply of compressed air and having one or more pistons located within the flexible resilient bellows or sleeves to cause compression and expansion as the vehicle experiences the road shocks. The pistons cause compression and expansion of the fluid within the spring sleeve with the sleeve being of a flexible material permitting the pistons to move axially with respect to each other within the interior of the sleeve. The ends of the sleeve usually are sealingly connected to the piston or supporting structure. Many of the pressure chamber forming sleeves of these prior art air springs are bellow shaped or have rolled ends to permit the pistons to move axially with respect to each other between a jounce or collapsed position and a rebound or expended position without damaging the flexible sleeve in which the pistons are located.
U.S. Pat. No. 2,926,011 shows an air spring having a variable contour piston which is connected between a vehicle under carriage and frame. A piston diaphram has inwardly directed portions and ends which are attached to a top piston plate and to a resting plate.
U.S. Pat. No. 2,985,445 discloses a pneumatic spring control device which comprises an air spring assembly having a dome shaped metal body with a peripheral lip and a circular bellows retainer ring. A spring piston is attached to the other end of the bellows assembly and is rigidly mounted to a vehicle wheel supporting arm to reciprocate with the wheel in an arcuate path into and out of the dome.
U.S. Pat. No. 2,978,256 shows a dual height suspension control mechanism having an air spring which includes an upper generally inverted cup shaped cylinder secured to the outer end of a frame member. A cylindrical piston moves into and out of the generally inverted dome-shaped assembly. The assembly and the cylinder are attached to each other by a single convolution flexible bellows having an inner bead portion engaging an inturned lip of the piston.
U.S. Pat. No. 3,046,000 discloses a vehicle suspension spring assembly which includes an inverted cup-shaped member and a hollow piston. The piston is rigidly secured to an outer wall of a hydraulic shock absorber cylinder and a flexible diaphram element of the rolling lobe type is attached at one end to the upper end of the piston and at its other end to a lower peripheral wall of a dome. When the spring assembly is deflected upwardly, a stiker moves upwardly and downwardly with a shock absorber casing along the axis of the piston rod without engaging a rubber buffer.
U.S. Pat. No. 3,074,709 shows an air suspension system for a motor vehicle which includes a movable piston in a housing. A flexible expansible material attaches the bead of a metallic cup to the bead of another element.
U.S. Pat. No. 4,518,154 discloses a pneumatic motor vehicle spring which includes cup-shaped pistons which are connected to each other by a flexible bellow. Relatively rigid sleeves are provided which extend about the exterior of the flexible bellows. Two pistons are elastically connected to provide an axial distance between the pistons as a function of the pressure within the volume defined by the spring.
Some other examples of prior art air springs for vehicles are shown in U.S. Pat. Nos. 3,154,318 and 3,895,787 and in U.K. Patent Application Nos. 2 028 463; 2 037 934; 2 043 831; and 2 044 395.
A common problem with known air spring constructions of the type shown in several of the above listed patents is that for many vehicles, a limited amount of space is available for mounting the air spring between the movable components of the vehicle. This seriously limits the operating height of the spring and limits the stroke distance of the pistons and sleeve required for the satisfactory operation of the spring for many vehicles on which the springs are mounted.
Therefore, the need has existed for an improved air spring construction which permits a normal vertical stroke movement with a reduced at-rest or operating height.